Pemphigoid represents a group of subepidermal blistering diseases characterized by autoantibodies against components of hemidesmosomes, organelles in basal keratinocytes that promote adhesion of epidermis to basement membrane (BM). Bullous pemphigoid antigen 2 (BPAG2), a type II transmembrane protein in hemidesmosomes, is a major autoantigen bound by such patients' autoantibodies. Our hypothesis is that autoantibodies against BPAG2 are pathogenic, that T cells provide crucial signals for production of such antibodies, and that antagonism of such antigen-specific T cells will abrogate production of pathogenic antibodies. To test this hypothesis, transgenic (Tg) mice expressing human BPAG2 (hBPAG2) in murine epidermal BM have been produced. Our goals are to use these mice to: a) assess the pathogenic activity of patient anti-hBPAG2 autoantibodies in vivo; b) elicit and characterize model immune responses of B and T cells to hBPAG2; c) develop an experimental animal model that mimics pemphigoid; and d) identify interventions that may modulate or antagonize immune responses to hBPAG2. Preliminary studies indicate that grafting hBPAG2 Tg skin onto syngeneic wild type mice elicits production of anti-hBPAG2 IgG that targets the same portion of this antigen that is bound by autoantibodies and T cell lines from patients with pemphigoid. Anti-hBPAG2 IgG did not develop in MHC class II -/- mice grafted with hBPAG2 Tg skin indicating that cognate interactions between T cell receptor/peptide-class II MHC determinants appear to be crucial for antigen-specific IgG production in this model. Preliminary studies also indicate that such antigen-specific responses in "immunized" wild type mice can be adoptively transferred to Tg mice expressing the antigen of interest (i.e., hBPAG2) in a tissue-specific and biologically relevant site in vivo (i.e., epidermal BM). Moreover, patient anti-BPAG2 autoantibodies bind epidermal BM in Tg skin, thus supporting the hypothesis that such mice can be used to assess the pathogenic activity of patient autoantibodies in vivo. Studies outlined in this proposal will build upon these observations to define primary immune responses to BPAG2, identify ways to block such responses, and develop relevant animal models of immunobullous diseases in which basic pathomechanisms can be defined and novel therapeutic interventions can be explored, tested, and refined.